Device and method for reducing effects of video artifacts

ABSTRACT

A method for reducing an effect of a video artifact includes adjusting a phase of a second imaging device&#39;s video clock signal so that a phase of the second imaging device&#39;s video synchronization signal matches a phase of a first imaging device&#39;s video synchronization signal. An endoscopic system includes a first imaging device, a second imaging device, a light source, and a controller that reduces an artifact in an image produced by the first imaging device. In some embodiments, the first imaging device faces the light source.

This application claims the benefit of U.S. Provisional PatentApplication No. 60/801,748, filed May 19, 2006, the entire disclosure ofwhich is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and method for reducingeffects of video artifacts.

BACKGROUND OF THE INVENTION

Multiple endoscopic devices with multiple cameras and light sources maybe used for medical procedures, inspection of small pipes, or remotemonitoring. For example, such an endoscopic device may be a medicalendoscope comprising a flexible tube, and a camera and a light sourcemounted on the distal end of the flexible tube. The endoscope isinsertable into an internal body cavity through a body orifice toexamine the body cavity and tissues for diagnosis. The tube of theendoscope has one or more longitudinal channels, through which aninstrument can reach the body cavity to take samples of suspicioustissues or to perform other surgical procedures such as polypectomy.

There are many types of endoscopes, and they are named in relation tothe organs or areas with which they are used. For example, gastroscopesare used for examination and treatment of the esophagus, stomach andduodenum; colonoscopes for the colon; bronchoscopes for the bronchi;laparoscopes for the peritoneal cavity; sigmoidoscopes for the rectumand the sigmoid colon; arthroscopes for joints; cystoscopes for theurinary bladder; and angioscopes for the examination of blood vessels.

Each endoscope has a single forward viewing camera mounted at the distalend of the flexible tube to transmit an image to an eyepiece or videocamera at the proximal end. The camera is used to assist a medicalprofessional in advancing the endoscope into a body cavity and lookingfor abnormalities. The camera provides the medical professional with atwo-dimensional view from the distal end of the endoscope. To capture animage from a different angle or in a different portion, the endoscopemust be repositioned or moved back and forth. Repositioning and movementof the endoscope prolongs the procedure and causes added discomfort,complications, and risks to the patient. Additionally, in an environmentsimilar to the lower gastro-intestinal tract, flexures, tissue folds andunusual geometries of the organ may prevent the endoscope's camera fromviewing all areas of the organ. The unseen area may cause a potentiallymalignant (cancerous) polyp to be missed.

This problem can be overcome by providing an auxiliary camera and anauxiliary light source. The auxiliary camera and light source can beoriented to face the main camera and light source, thus providing animage of areas not viewable by the endoscope's main camera. Thisarrangement of cameras and light sources can provide both front and rearviews of an area or an abnormality. In the case of polypectomy where apolyp is excised by placing a wire loop around the base of the polyp,the camera arrangement allows better placement of the wire loop tominimize damage to the adjacent healthy tissue.

The two cameras may be based on different technologies and may havedifferent characteristics. In many cases, the main camera is a chargecoupled device (CCD) camera that requires a very intense light sourcefor illumination. Such as a light source may be a fiber optic bundle.The auxiliary camera may be a complementary metal oxide semiconductor(CMOS) camera with a light emitting diode (LED) to provide illumination.

SUMMARY OF THE INVENTION

The inventors of the present application have observed that, whenmultiple imaging and light emitting devices are used as described in thebackground section of the present specification, artifacts may appear onthe video images produced by the imaging devices. One example of theobserved artifacts is a “thin line” near the top edge of a video imagegenerated by a main endoscope's CCD imaging device, when the CCD imagingdevice is used in pair with retrograde imaging and light emittingdevices.

The inventors believe that this “thin line” artifact is caused by howimages are captured and/or processed by the CCD imaging device.Alternatively or additionally, the artifact may be related the videoprocessing circuitry. In a CCD camera system, image data are capturedand/or processed a single row of the image at a time. As a result, ifthere is a bright light source such as the retrograde light emittingdevice, individual pixels of the image can succumb to charge “leaks”which can spill over into the other light receptors in the same row.This may cause loss of portions of the video image and appearance of a“thin line” in the video image.

The present invention can be used to reduce the effects of the “thinline” artifact. In accordance with one aspect of the invention, anendoscopic system includes a first imaging device, a second imagingdevice, a light source, and a controller that reduces an artifact in animage produced by the first imaging device. In some embodiments, thefirst imaging device faces the light source.

In one preferred embodiment, the controller adjusts a frequency of thesecond imaging device's video clock signal so that a frequency of thesecond imaging device's video synchronization signal matches a frequencyof the first imaging device's video synchronization signal.

In another preferred embodiment, the controller adjusts a phase of thesecond imaging device's video clock signal to vary the phase between thesecond imaging device's video synchronization signal and the firstimaging device's video synchronization signal. The phase between the twovideo synchronization signals may be zero or nonzero.

In still another preferred embodiment, the controller synchronizes aduty cycle of the light source to turn on the light source only when thefirst imaging device is in a vertical blanking interval to reduce thesize of the artifact.

In yet another preferred embodiment, the controller moves the artifactby adjusting a pulse width and/or delay timing of the light source.Preferably, the controller moves the artifact vertically.

In still yet another preferred embodiment, wherein the controllerincludes a phase lock loop circuit that is connected to the firstimaging device to receive a video synchronization signal of the firstimaging device and connected to the second imaging device to receive avideo synchronization signal of the second imaging device and to send avideo clock signal for the second imaging device, wherein the phase lockloop circuit adjusts a phase of the second imaging device's video clocksignal so that a phase of the second imaging device's videosynchronization signal matches a phase of the first imaging device'svideo synchronization signal.

In a further preferred embodiment, the phase lock loop circuit adjusts afrequency of the second imaging device's video clock signal so that afrequency of the second imaging device's video synchronization signalmatches a frequency of the first imaging device's video synchronizationsignal.

In a still further preferred embodiment, the controller includes a lightsource driver, and the light source driver is connected to the phaselock loop circuit to receive the video clock signal. Preferably, thelight source driver synchronizes a duty cycle of the light source toturn on the light source only when the first imaging device is in avertical blanking interval to reduce the size of the artifact.

In a yet further preferred embodiment, the light source driver moves theartifact by adjusting a pulse width and/or delay timing of the lightsource. Preferably, the controller moves the artifact vertically.

In a still yet further preferred embodiment, the phase lock loop circuitincludes a sync separator that is connected to the first imaging deviceto receive the video synchronization signal of the first imaging deviceand connected to the second imaging device to receive the videosynchronization signal of the second imaging device. Preferably, thesync separator extracts a vertical synchronization signal from the videosynchronization signal of the first imaging device and another verticalsynchronization signal from the video synchronization signal of thesecond imaging device.

In another preferred embodiment, the phase lock loop circuit includes aphase detector that is connected to the sync separator to receive thevertical synchronization signals. Preferably, the phase detectorcomputes the phase difference between the vertical synchronizationsignals using the vertical synchronization signal of the first imagingdevice as a reference signal.

In still another preferred embodiment, the phase lock loop circuitincludes a low pass filter that is connected to the phase detector toreceive the phase difference and that averages the phase difference toreduce the noise content of the phase difference.

In yet another preferred embodiment, the phase lock loop circuitincludes an oscillator that is connected to the low pass filter toreceive the averaged phase difference and that creates the video clocksignal.

In accordance with another aspect of the invention, an endoscopic systemincludes a first imaging device, a second imaging device, a lightsource, and a controller that varies a phase difference between videosynchronization signals of the first and second imaging devices toreduce an artifact in an image produced by the first imaging device.

In accordance with still another aspect of the invention, an endoscopicsystem includes a first imaging device, a first light source, a secondimaging device, a second light source, and a controller. The firstimaging device and light source may face the second imaging device andlight source. Preferably, the controller includes a phase lock loopcircuit that is connected to the first imaging device to receive a videosynchronization signal of the first imaging device and connected to thesecond imaging device to receive a video synchronization signal of thesecond imaging device and to send a video clock signal for the secondimaging device so that image frames of the imaging devices have the samefrequency and are in phase. The first imaging device and light sourcemay be powered on during one half of the frame period, and the secondimaging device and light source are powered on during the other half ofthe frame period.

In a preferred embodiment, the frame frequency is sufficiently high suchthat eyes cannot sense that the first and second imaging devices andtheir light sources are intermittently powered on and off.

In accordance with a further aspect of the invention, a method forreducing an effect of a video artifact includes adjusting a phase of asecond imaging device's video clock signal so that a phase of the secondimaging device's video synchronization signal matches a phase of a firstimaging device's video synchronization signal.

In a preferred embodiment, the method further includes adjusting afrequency of the second imaging device's video clock signal so that afrequency of the second imaging device's video synchronization signalmatches a frequency of the first imaging device's video synchronizationsignal.

In another preferred embodiment, the method further includessynchronizing a duty cycle of a light source to turn on the light sourceonly when the first imaging device is in a vertical blanking interval toreduce the size of the artifact, wherein the light source faces thefirst imaging device.

In yet another preferred embodiment, the method further includes movingthe artifact by adjusting a pulse width and/or delay timing of the lightsource. Preferably, the moving step includes moving the artifactvertically.

In still yet another preferred embodiment, the adjusting step includesextracting a vertical synchronization signal from the videosynchronization signal of the first imaging device and another verticalsynchronization signal from the video synchronization signal of thesecond imaging device.

In a further preferred embodiment, the adjusting step includes computingthe phase difference between the vertical synchronization signals usingthe vertical synchronization signal of the first imaging device as areference signal.

In a still further preferred embodiment, the adjusting step includesaveraging the phase difference to reduce the noise content of the phasedifference.

In a yet further preferred embodiment, the adjusting step includescreating the video clock signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of an endoscope with an imaging assemblyaccording to one embodiment of the present invention.

FIG. 2 shows a perspective view of the distal end of an insertion tubeof the endoscope of FIG. 1.

FIG. 3 shows a perspective view of the imaging assembly shown in FIG. 1.

FIG. 4 shows a perspective view of the distal ends of the endoscope andimaging assembly of FIG. 1.

FIG. 5 shows a schematic diagram of a controller that, together with theendoscope of FIG. 1, forms an endoscope system.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates an exemplary endoscope 10 of the present invention.This endoscope 10 can be used in a variety of medical procedures inwhich imaging of a body tissue, organ, cavity or lumen is required. Thetypes of procedures include, for example, anoscopy, arthroscopy,bronchoscopy, colonoscopy, cystoscopy, EGD, laparoscopy, andsigmoidoscopy.

The endoscope 10 of FIG. 1 includes an insertion tube 12 and an imagingassembly 14, a section of which is housed inside the insertion tube 12.As shown in FIG. 2, the insertion tube 12 has two longitudinal channels16. In general, however, the insertion tube 12 may have any number oflongitudinal channels. An instrument can reach the body cavity throughone of the channels 16 to perform any desired procedures, such as totake samples of suspicious tissues or to perform other surgicalprocedures such as polypectomy. The instruments may be, for example, aretractable needle for drug injection, hydraulically actuated scissors,clamps, grasping tools, electrocoagulation systems, ultrasoundtransducers, electrical sensors, heating elements, laser mechanisms andother ablation means. In some embodiments, one of the channels can beused to supply a washing liquid such as water for washing. Another orthe same channel may be used to supply a gas, such as CO₂ or air intothe organ. The channels 16 may also be used to extract fluids or injectfluids, such as a drug in a liquid carrier, into the body. Variousbiopsy, drug delivery, and other diagnostic and therapeutic devices mayalso be inserted via the channels 16 to perform specific functions.

The insertion tube 12 preferably is steerable or has a steerable distalend region 18 as shown in FIG. 1. The length of the distal end region 18may be any suitable fraction of the length of the insertion tube 12,such as one half, one third, one fourth, one sixth, one tenth, or onetwentieth. The insertion tube 12 may have control cables (not shown) forthe manipulation of the insertion tube 12. Preferably, the controlcables are symmetrically positioned within the insertion tube 12 andextend along the length of the insertion tube 12. The control cables maybe anchored at or near the distal end 36 of the insertion tube 12. Eachof the control cables may be a Bowden cable, which includes a wirecontained in a flexible overlying hollow tube. The wires of the Bowdencables are attached to controls 20 in the handle 22. Using the controls20, the wires can be pulled to bend the distal end region 18 of theinsertion tube 12 in a given direction. The Bowden cables can be used toarticulate the distal end region 18 of the insertion tube 12 indifferent directions.

As shown in FIG. 1, the endoscope 10 may also include a control handle22 connected to the proximal end 24 of the insertion tube 12.Preferably, the control handle 22 has one or more ports and/or valves(not shown) for controlling access to the channels 16 of the insertiontube 12. The ports and/or valves can be air or water valves, suctionvalves, instrumentation ports, and suction/instrumentation ports. Asshown in FIG. 1, the control handle 22 may additionally include buttons26 for taking pictures with an imaging device on the insertion tube 12,the imaging assembly 14, or both. The proximal end 28 of the controlhandle 22 may include an accessory outlet 30 (FIG. 1) that providesfluid communication between the air, water and suction channels and thepumps and related accessories. The same outlet 30 or a different outletcan be used for electrical lines to light and imaging components at thedistal end of the endoscope 10.

As shown in FIG. 2, the endoscope 10 may further include an imagingdevice 32 and light sources 34, both of which are disposed at the distalend 36 of the insertion tube 12. The imaging device 32 may include, forexample, a lens, single chip sensor, multiple chip sensor or fiber opticimplemented devices. The imaging device 32, in electrical communicationwith a processor and/or monitor, may provide still images or recorded orlive video images. The light sources 34 preferably are equidistant fromthe imaging device 32 to provide even illumination. The intensity ofeach light source 34 can be adjusted to achieve optimum imaging. Thecircuits for the imaging device 32 and light sources 34 may beincorporated into a printed circuit board (PCB).

As shown in FIGS. 3 and 4, the imaging assembly 14 may include a tubularbody 38, a handle 42 connected to the proximal end 40 of the tubularbody 38, an auxiliary imaging device 44, a link 46 that providesphysical and/or electrical connection between the auxiliary imagingdevice 44 to the distal end 48 of the tubular body 38, and an auxiliarylight source 50 (FIG. 4). The auxiliary light source 50 may be an LEDdevice.

As shown in FIG. 4, the imaging assembly 14 of the endoscope 10 is usedto provide an auxiliary imaging device at the distal end of theinsertion tube 12. To this end, the imaging assembly 14 is placed insideone of the channels 16 of the endoscope's insertion tube 12 with itsauxiliary imaging device 44 disposed beyond the distal end 36 of theinsertion tube 12. This can be accomplished by first inserting thedistal end of the imaging assembly 14 into the insertion tube's channel16 from the endoscope's handle 18 and then pushing the imaging assembly14 further into the assembly 14 until the auxiliary imaging device 44and link 46 of the imaging assembly 14 are positioned outside the distalend 36 of the insertion tube 12 as shown in FIG. 4.

Each of the main and auxiliary imaging devices 32, 44 may be anelectronic device which converts light incident on photosensitivesemiconductor elements into electrical signals. The imaging sensor maydetect either color or black-and-white images. The signals from theimaging sensor can be digitized and used to reproduce an image that isincident on the imaging sensor. Two commonly used types of image sensorsare Charge Coupled Devices (CCD) such as a VCC-5774 produced by Sanyo ofOsaka, Japan and Complementary Metal Oxide Semiconductor (CMOS) camerachips such as an OVT 6910 produced by OnmiVision of Sunnyvale, Calif.Preferably, the main imaging device 32 is a CCD imaging device, and theauxiliary imaging device 44 is a CMOS imaging device.

When the imaging assembly 14 is properly installed in the insertion tube12, the auxiliary imaging device 44 of the imaging assembly 14preferably faces backwards towards the main imaging device 32 asillustrated in FIG. 4. The auxiliary imaging device 44 may be orientedso that the auxiliary imaging device 44 and the main imaging device 32have adjacent or overlapping viewing areas. Alternatively, the auxiliaryimaging device 44 may be oriented so that the auxiliary imaging device44 and the main imaging device 32 simultaneously provide different viewsof the same area. Preferably, the auxiliary imaging device 44 provides aretrograde view of the area, while the main imaging device 32 provides afront view of the area. However, the auxiliary imaging device 44 couldbe oriented in other directions to provide other views, including viewsthat are substantially parallel to the axis of the main imaging device32.

As shown in FIG. 4, the link 46 connects the auxiliary imaging device 44to the distal end 48 of the tubular body 38. Preferably, the link 46 isa flexible link that is at least partially made from a flexible shapememory material that substantially tends to return to its original shapeafter deformation. Shape memory materials are well known and includeshape memory alloys and shape memory polymers. A suitable flexible shapememory material is a shape memory alloy such as nitinol. The flexiblelink 46 is straightened to allow the distal end of the imaging assembly14 to be inserted into the proximal end of assembly 14 of the insertiontube 12 and then pushed towards the distal end 36 of the insertion tube12. When the auxiliary imaging device 44 and flexible link 46 are pushedsufficiently out of the distal end 36 of the insertion tube 12, theflexible link 46 resumes its natural bent configuration as shown in FIG.3. The natural configuration of the flexible link 46 is theconfiguration of the flexible link 46 when the flexible link 46 is notsubject to any force or stress. When the flexible link 46 resumes itsnatural bent configuration, the auxiliary imaging device 44 facessubstantially back towards the distal end 36 of the insertion tube 12 asshown in FIG. 5.

In the illustrated embodiment, the auxiliary light source 50 of theimaging assembly 14 is placed on the flexible link 46, in particular onthe curved concave portion of the flexible link 46. The auxiliary lightsource 50 provides illumination for the auxiliary imaging device 44 andmay face substantially the same direction as the auxiliary imagingdevice 44 as shown in FIG. 4.

The endoscope of the present invention, such as the endoscope 10 shownin FIG. 1, may be part of an endoscope system that also includes acontroller. The term “controller” as used in this specification isbroadly defined. In some embodiments, for example, the term “controller”may simply be a signal processing unit.

The controller can be used for, among others, reducing or eliminatingthe “thin line” artifacts described above. FIG. 5 illustrates apreferred embodiment 52 of the controller. The preferred controller 52includes a phase lock loop (PLL) circuit 54. The PLL circuit 54 includesa sync separator 56, a phase detector 58, a low pass filter 60, and anoscillator 62.

The sync separator 56 is connected to each of the main and auxiliaryimaging devices 32, 44 to receive a video synchronization signal 64 fromeach imaging device 32, 44. The sync separator 56 extracts a verticalsynchronization signal from each video synchronization signal 64. Thephase detector 58 is connected to the sync separator 56 and receives thevertical synchronization signals from the sync separator 56. The phasedetector 56 then computes the phase difference between the verticalsynchronization signals using the vertical synchronization signal of themain imaging device 32 as the reference signal. The low pass filter 60is connected to the phase detector 58 and receives the phase differencefrom the phase detector 58. The low pass filter 60 averages the phasedifference to reduce the noise content of the phase difference. Theoscillator 62 is connected to the low pass filter 60 and receives theaveraged phase difference. Based on the averaged phase difference, theoscillator 62 creates an output signal that matches the frequency andphase of the vertical synchronization signal of the main imaging device32. This output signal of the PLL circuit 54 may be then amplified andsent to the auxiliary imaging device 44 as a video clock signal 66. Thisfeedback control loop adjusts the phase and/or frequency of theauxiliary imaging device's video clock so that the phase and frequencyof the auxiliary imaging device's video synchronization signal 64 matchthose of the main imaging device 32's video synchronization signal 64.In other words, the two imaging devices 32, 44 have the same framefrequency and frame phase.

The preferred controller 52 shown in FIG. 5 may also include anauxiliary light source driver 68 that is used to “pulse” the auxiliarylight source 50. A “pulsed” light source is not constantly powered on.Instead, it is turned on and off intermittently at a certain frequency.The frequency, phase and duty cycle (pulse width) of the auxiliary lightsource 50 can be adjusted by the auxiliary light source driver 68. inaddition, the output signal of the PLL circuit 54 may also be sent tothe auxiliary light source driver 68 to match the frequency of theauxiliary light source 50 with that of the imaging devices 32, 44.

The inventors of the present application have discovered that the sizeand position of the artifact on an image produced by the main imagingdevice 32 may be adjusted by varying at least the duty cycle of theauxiliary light source 50 and by varying at least the phase of theauxiliary light source 50 relative to the imaging devices 32, 44. Forexample, the duty cycle of the auxiliary light source 50 may be adjustedto vary at least the size of the artifact. In particular, the size ofthe artifact may be reduced by decreasing the duty cycle of theauxiliary light source 50. In the case of the “thin line” artifact, thelength of the artifact may be reduced by decreasing the duty cycle ofthe auxiliary light source 50.

For another example, the artifact on an image produced by the mainimaging device 32 may be moved, such as vertically, by varying at leastthe phase of the auxiliary light source 50 relative to the imagingdevices 32, 44. The controller 52 may allow a user to adjust the phaseof the auxiliary light source 50 to move the artifact to a region ofnon-interest in the image such as the location of the auxiliary lightsource 50.

For a further example, the duty cycle and/or phase of the auxiliarylight source 50 may be adjusted so that the auxiliary light source 50 ispowered on only when the main imaging device 32 is in a verticalblanking interval, resulting in a reduction in the size of the artifact.

Similarly, using the above-described processes and devices, the sizeand/or position of an artifact on an image produced by the auxiliaryimaging device 44 may be adjusted by varying at least the duty cycle ofthe main light source 34 and by varying at least the phase of the mainlight source 34 relative to the imaging devices 32, 44.

In addition, an artifact on an image produced by one of the imagedevices 32, 44 may also be minimized by introducing a phase differencebetween the video synchronization signals of the main and auxiliaryimaging devices 32, 44 (i.e., introducing a phase delay between theframe rates of the two video signals). The PLL circuit 54 may be used tomaintain the desired phase difference between the video synchronizationsignals. The controller 52 may be used to adjust the phase differencebetween the video synchronization signals to minimize the artifact.

The auxiliary imaging device 44 and its light source 50 may be connectedto the controller 52 (not shown) via electrical conductors that extendfrom the imaging device 44 and light source 50; through the link 46,tubular body 38, and handle 42; to the controller 52. The electricalconductors may carry power and control commands to the auxiliary imagingdevice 44 and its light source 50 and image signals from the auxiliaryimaging device 44 to the controller 52.

The controller 52 may be used to adjust the parameters of the imagingdevices 32, 44 and their light sources 34, 50, such as brightness,exposure time and mode settings. The adjustment can be done by writingdigital commands to specific registers controlling the parameters. Theregisters can be addressed by their unique addresses, and digitalcommands can be read from and written to the registers to change thevarious parameters. The controller 52 can change the register values bytransmitting data commands to the registers.

In an alternate embodiment, the controller 52 may be used to reducelight interference between the main imaging device 32 and light source34 and the auxiliary imaging device 44 and light source 50. Since themain imaging device 32 and light source 34 face the auxiliary imagingdevice 44 and light source 50, the main light source 34 interferes withthe auxiliary imaging device 44, and the auxiliary light source 50interferes with the main imaging device 32. Light interference is theresult of the light from a light source being projected directly onto animaging device. This may cause light glare, camera blooming, or oversaturation of light, resulting in inferior image quality.

To reduce or eliminate light interference, the imaging devices 32, 44and their light sources 34, 50 may be turned on and off alternately. Inother words, when the main imaging device 32 and light source 34 areturned on, the auxiliary imaging device 44 and light source 50 areturned off. And when the main imaging device 32 and light sources 34 areturned off, the auxiliary imaging device 44 and light source 50 areturned on. Preferably, the imaging devices 32, 44 and their lightsources 34, 50 are turned on and off at a sufficiently high frequencythat eyes do not sense that the light sources 34, 50 are being turned onand off.

The timing of powering on and off the imaging devices 32, 44 and theirlight sources 34, 50 can be accomplished using the PLL circuit 54 shownin FIG. 5. The PLL circuit 54 may be employed to match the framefrequencies and phases of the imaging devices 32, 44 as discussed above.Then, the main imaging device 32 and light source 34 are powered onduring one half of the frame period, and the auxiliary imaging device 44and light source 50 are powered on during the other half of the frameperiod.

The above-described processes and devices may also be used when thereare more than two imaging devices and two light sources and when theimaging devices and light sources are on two or more endoscopes.

1. An endoscopic system comprising: a first imaging device; a secondimaging device; a light source; and a controller that reduces anartifact in an image produced by the first imaging device.
 2. Theendoscopic system of claim 1, wherein the first imaging device faces thelight source.
 3. The endoscopic system of claim 1, wherein thecontroller adjusts a phase of the second imaging device's video clocksignal so that a phase between the second imaging device's videosynchronization signal and the first imaging device's videosynchronization signal is about zero.
 4. The endoscopic system of claim1, wherein the controller adjusts a frequency of the second imagingdevice's video clock signal so that a frequency of the second imagingdevice's video synchronization signal matches a frequency of the firstimaging device's video synchronization signal.
 5. The endoscopic systemof claim 4, wherein the controller adjusts a phase of the second imagingdevice's video clock signal so that a phase between the second imagingdevice's video synchronization signal and the first imaging device'svideo synchronization signal is about zero.
 6. The endoscopic system ofclaim 5, wherein the controller moves the artifact by adjusting a phaseof the light source relative to the imaging devices.
 7. The endoscopicsystem of claim 6, wherein the controller moves the artifact vertically.8. The endoscopic system of claim 5, wherein the controller reduces asize of the artifact by decreasing the duty cycle of the light source.9. The endoscopic system of claim 5, wherein the controller adjusts aphase of the light source so that the light source is powered on onlywhen the first imaging device is in a vertical blanking interval. 10.The endoscopic system of claim 1, wherein the controller comprising: aphase lock loop circuit that is connected to the first imaging device toreceive a video synchronization signal of the first imaging device andconnected to the second imaging device to receive a videosynchronization signal of the second imaging device and to send a videoclock signal for the second imaging device.
 11. The endoscopic system ofclaim 10, wherein the phase lock loop circuit adjusts a phase of thesecond imaging device's video clock signal so that a phase between thesecond imaging device's video synchronization signal and the firstimaging device's video synchronization signal is about zero.
 12. Theendoscopic system of claim 10, wherein the phase lock loop circuitadjusts a frequency of the second imaging device's video clock signal sothat a frequency of the second imaging device's video synchronizationsignal matches a frequency of the first imaging device's videosynchronization signal.
 13. The endoscopic system of claim 12, whereinthe phase lock loop circuit adjusts a phase of the second imagingdevice's video clock signal so that a phase between the second imagingdevice's video synchronization signal and the first imaging device'svideo synchronization signal is about zero.
 14. The endoscopic system ofclaim 13, wherein the controller includes a light source driver, whereinthe light source driver is connected to the phase lock loop circuit toreceive the video clock signal.
 15. The endoscopic system of claim 14,wherein the light source driver moves the artifact by adjusting a phaseof the light source relative to the imaging devices.
 16. The endoscopicsystem of claim 15, wherein the light source driver moves the artifactvertically.
 17. The endoscopic system of claim 14, wherein the lightsource driver reduces a size of the artifact by decreasing the dutycycle of the light source.
 18. The endoscopic system of claim 14,wherein the light source driver adjusts a phase of the light source sothat the light source is powered on only when the first imaging deviceis in a vertical blanking interval.
 19. An endoscopic system comprising:a first imaging device; a second imaging device; a light source; and acontroller that adjusts a frequency of the second imaging device's videoclock signal so that a frequency of the second imaging device's videosynchronization signal matches a frequency of the first imaging device'svideo synchronization signal and that varies a phase difference betweenvideo synchronization signals of the first and second imaging devices toreduce an artifact in an image produced by the first imaging device. 20.A device for reducing an effect of an artifact produced by an endoscopicsystem including a first imaging device, a second imaging device, and alight source, the device comprising: a phase lock loop circuit that isconnected to the first imaging device to receive a video synchronizationsignal of the first imaging device and connected to the second imagingdevice to receive a video synchronization signal of the second imagingdevice and to send a video clock signal for the second imaging device.21. The device of claim 20, wherein the phase lock loop circuit adjustsa phase of the second imaging device's video clock signal so that aphase between the second imaging device's video synchronization signaland the first imaging device's video synchronization signal is aboutzero.
 22. The device of claim 20, wherein the phase lock loop circuitadjusts a frequency of the second imaging device's video clock signal sothat a frequency of the second imaging device's video synchronizationsignal matches a frequency of the first imaging device's videosynchronization signal.
 23. The device of claim 22, wherein the phaselock loop circuit adjusts a phase of the second imaging device's videoclock signal so that a phase between the second imaging device's videosynchronization signal and the first imaging device's videosynchronization signal is about zero.
 24. The device of claim 23,further comprising a light source driver, wherein the light sourcedriver is connected to the phase lock loop circuit to receive the videoclock signal.
 25. The device of claim 24, wherein the light sourcedriver moves the artifact by adjusting a phase of the light sourcerelative to the imaging devices.
 26. The device of claim 25, wherein thelight source driver moves the artifact vertically.
 27. The device ofclaim 24, wherein the light source driver reduces a size of the artifactby decreasing the duty cycle of the light source.
 28. The device ofclaim 24, wherein the light source driver adjusts a phase of the lightsource so that the light source is powered on only when the firstimaging device is in a vertical blanking interval.
 29. A method forreducing an effect of a video artifact, comprising adjusting a frequencyof a second imaging device's video clock signal so that a frequency ofthe second imaging device's video synchronization signal matches afrequency of a first imaging device's video synchronization signal. 30.The method of claim 29, further comprising adjusting a phase of thesecond imaging device's video clock signal so that a phase of the secondimaging device's video synchronization signal matches a phase of thefirst imaging device's video synchronization signal.
 31. The method ofclaim 30, further comprising moving the artifact by adjusting a phase ofa light source relative to the imaging devices.
 32. The method of claim32, wherein the moving step includes moving the artifact vertically. 33.The method of claim 30, further comprising reducing a size of theartifact by decreasing the duty cycle of a light source.
 34. The methodof claim 37, further comprising adjusting a phase of the light source sothat the light source is powered on only when the first imaging deviceis in a vertical blanking interval.
 35. An endoscopic system comprising:a first imaging device; a second imaging device; a light source; and acontroller that adjusts a frequency of the second imaging device's videoclock signal so that a frequency of the second imaging device's videosynchronization signal matches a frequency of the first imaging device'svideo synchronization signal and that varies a phase difference betweenvideo synchronization signals of the first and second imaging devices.36. An endoscopic system controller including a first imaging device, asecond imaging device, and a light source, the controller devicecomprising: a phase lock loop circuit that is connected to the firstimaging device to receive a video synchronization signal of the firstimaging device and connected to the second imaging device to receive avideo synchronization signal of the second imaging device and to send avideo clock signal for the second imaging device.
 37. The device ofclaim 36, wherein the phase lock loop circuit adjusts a phase of thesecond imaging device's video clock signal so that a phase between thesecond imaging device's video synchronization signal and the firstimaging device's video synchronization signal is about zero.
 38. Thedevice of claim 37, wherein the phase lock loop circuit adjusts afrequency of the second imaging device's video clock signal so that afrequency of the second imaging device's video synchronization signalmatches a frequency of the first imaging device's video synchronizationsignal.
 39. The device of claim 38, wherein the phase lock loop circuitadjusts a phase of the second imaging device's video clock signal sothat a phase between the second imaging device's video synchronizationsignal and the first imaging device's video synchronization signal isabout zero.
 40. The device of claim 39, further comprising a lightsource driver, wherein the light source driver is connected to the phaselock loop circuit to receive the video clock signal.
 41. The device ofclaim 37, wherein the light source driver adjusting a phase of the lightsource relative to the imaging devices.
 43. The device of claim 37,wherein the light source driver drives the light for only a portion of afull duty cycle.
 44. The device of claim 37, wherein the light sourcedriver adjusts a phase of the light source so that the light source ispowered on only when the first imaging device is in a vertical blankinginterval.
 45. An endoscopic system comprising: a first imaging device; afirst light source; a second imaging device; a second light source,wherein the first imaging device and light source face the secondimaging device and light source; and a controller including a phase lockloop circuit that is connected to the first imaging device to receive avideo synchronization signal of the first imaging device and connectedto the second imaging device to receive a video synchronization signalof the second imaging device and to send a video clock signal for thesecond imaging device so that image frames of the imaging devices havethe same frequency and are in phase, wherein the first imaging deviceand light source are powered on during one half of the frame period, andwherein the second imaging device and light source are powered on duringthe other half of the frame period.
 46. The system of claim 45, whereinthe frame frequency is sufficiently high such that eyes cannot sensethat the first and second imaging devices and their light sources areintermittently powered on and off.
 47. An endoscopic system comprising:a first imaging device; a second imaging device; a first light source; asecond light source, and a controller that adjusts a frequency of thesecond imaging device's video clock signal so that a frequency of thesecond imaging device's video synchronization signal matches a frequencyof the first imaging device's video synchronization signal and thatvaries the phase difference between video synchronization signals of thefirst and second imaging devices to be of opposite phase.
 48. Anendoscopic system controller including a first imaging device, a secondimaging device, a first light source, a second light source, thecontroller device comprising: a phase lock loop circuit that isconnected to the first imaging device to receive a video synchronizationsignal of the first imaging device and connected to the second imagingdevice to receive a video synchronization signal of the second imagingdevice and to send a video clock signal for the second imaging device.49. The device of claim 48, wherein the phase lock loop circuit adjustsa phase of the second imaging device's video clock signal so that aphase between the second imaging device's video synchronization signaland the first imaging device's video synchronization signal is about180° out of phase.
 50. The device of claim 49, wherein the phase lockloop circuit adjusts a frequency of the second imaging device's videoclock signal so that a frequency of the second imaging device's videosynchronization signal matches a frequency of the first imaging device'svideo synchronization signal.
 51. The device of claim 50, wherein thephase lock loop circuit adjusts a phase of the second imaging device'svideo clock signal so that a phase between the second imaging device'svideo synchronization signal and the first imaging device's videosynchronization signal is about opposite.
 52. The device of claim 51,further comprising a first light source driver and a second lightsource, wherein the first light source driver is connected to the phaselock loop circuit to receive the video clock signal.
 53. The device ofclaim 49, wherein the first light source driver adjusting a phase of thefirst light source relative to the first imaging devices and the secondlight source driver adjusts a phase of the second light source relativeto the first imaging device
 54. The device of claim 49, wherein thelight sources driver drives the lights for only a portion of a full dutycycle.
 55. The device of claim 49, wherein the first light source driveradjusts a phase of the first light source so that the first light sourceis powered on only when the first imaging device is acquiring an image,and wherein the second light source driver adjusts a phase of the secondlight source so that the second light source is powered on only when thesecond imaging device is acquiring an image.
 56. The device of claim 53,where the first light source driver and second light source driver areof opposite phase
 57. An endoscopic system comprising: a first imagingdevice; a first light source; a second imaging device; a second lightsource, wherein the first imaging device and light source face thesecond imaging device and light source; and a controller including aphase lock loop circuit that is connected to the first imaging device toreceive a video synchronization signal of the first imaging device andconnected to the second imaging device to receive a videosynchronization signal of the second imaging device and to send a videoclock signal for the second imaging device so that image frames of theimaging devices have the same frequency and are in phase, wherein thefirst imaging device acquires an image and the first light source ispowered on during one half of the frame period, and wherein the secondimaging device acquires an image and the second light source is poweredon during the other half of the frame period.
 58. The system of claim57, wherein the frame frequency is sufficiently high such that eyescannot sense that the first and second imaging devices and their lightsources are intermittently utilized.
 59. A method for reducing lightinterference between a first imaging device and light source and asecond imaging device and light source of an endoscopic system, whereinthe first imaging device and light source face the second imaging deviceand light source, the method comprising: using a phase lock loop circuitto receive a video synchronization signal of the first imaging deviceand to receive a video synchronization signal of the second imagingdevice and to send a video clock signal for the second imaging device sothat image frames of the imaging devices have the same frequency and arein phase; and powering the first imaging device and light source onduring one half of the frame period, and powering the second imagingdevice and light source on during the other half of the frame period.60. A method for reducing light interference between a first imagingdevice and light source and a second imaging device and light source ofan endoscopic system, wherein the first imaging device and light sourceface the second imaging device and light source, the method comprising:adjusting a frequency of the second imaging device's video clock signalso that a frequency of the second imaging device's video synchronizationsignal matches a frequency of the first imaging device's videosynchronization signal; adjusting the phase difference between the videosynchronization signals of the first and second imaging devices to be ofopposite phase.